The Art of Modeling Stellar Mergers and the Case of the B[e] Supergiant R4 in the Small Magellanic Cloud

Abstract

Most massive stars exchange mass with a companion, leading to evolution which is altered drastically from that expected of stars in isolation. Such systems result from unusual binary evolution pathways and can place stringent constraints on the physics of these interactions. We use the R4 binary system's B[e] supergiant, which has been postulated to be the product of a stellar merger, to guide our understanding of such outcomes by comparing observations of R4 to the results of simulating a merger with the 3D hydrodynamics code FLASH. Our approach tailors the simulation initial conditions to observed properties of R4 and implements realistic stellar profiles from the 1D stellar evolution code MESA onto the 3D grid, resolving the merger inspiral to within 0.02 R e. We map the merger remnant into MESA to track its evolution on the H-R diagram over a period of 10 4 yr. This generates a model for a B[e] supergiant with stellar properties, age, and nebula structure in qualitative agreement with those of the R4 system. Our calculations provide evidence to support the idea that R4ʼs B[e] supergiant was originally a member of a triple system in which the inner binary merged after its most massive member evolved off the main sequence, producing a new object of similar mass but significantly more luminosity than the A supergiant companion. The code framework presented in this paper, which was constructed to model tidal encounters, can be used to generate accurate models of a wide variety of merger stellar remnants.

Detailed evolutionary models of massive contact binaries – I. Model grids and synthetic populations for the Magellanic Clouds

“…Investigating the evolution of contact binaries is required to estimate the fraction of the population of binary systems that will merge on the main sequence (MS), or survive it without merging. Those that do merge before either star forms a compact object may lead to fast-rotating single stars which may become progenitors of long duration −ray bursts Woosley & Bloom 2006;Yoon et al 2006;Meynet & Maeder 2007;Dessart et al 2008;van Marle, A. J. et al 2008;Szécsi 2017;Aguilera-Dena et al 2018) , B[e]/sgB[e] stars (e.g., Podsiadlowski et al 2006;Justham et al 2014;Wu et al 2020), blue supergiant progenitors of Type II supernovae such as SN 1987A (Podsiadlowski et al 1992;Menon & Heger 2017;Urushibata et al 2018;Menon et al 2019) and superluminous supernovae (Justham et al 2014;Sukhbold et al 2016;Aguilera-Dena et al 2020), pulsational pair instability supernovae (Langer 1991;Heger et al 2003;Langer et al 2007;Woosley et al 2007;Chatzopoulos & Wheeler 2012;Vigna-Gómez et al 2019) or magnetic stars (Schneider et al 2016(Schneider et al , 2019.…”

Transient Stellar Collisions as Multimessenger Probes: Nonthermal, Gravitational-wave Emission and the Cosmic Ladder Argument

“…With "collisional" we mean in general mutual gravitational deflections that lead to an exchange of energy and angular momentum, but also in particular genuine contact collisions. The possibility that collisions between stars play a fundamental role both in explaining particular observations and in the global influence of dense stellar systems has been studied with dedicated numerical studies (Spitzer & Saslaw 1966;Sanders 1970;Benz & Hills 1987, 1992David et al 1987aDavid et al , 1987bDavies et al 1991Davies et al , 1998Murphy et al 1991;Lai et al 1993;Lombardi et al 1995Lombardi et al , 1996Bailey & Davies 1999;Lombardi et al 2002;Shara 2002;Adams et al 2004;Trac et al 2007;Dale et al 2009;Wu et al 2020;Mastrobuono-Battisti et al 2021;Vergara et al 2021).…”

The Formation of Discs in the Interior of AGB Stars from the Tidal Disruption of Planets and Brown Dwarfs

“…To verify that these assumptions are reasonable and to obtain further insight, we numerically simulate the dynamics of the tidal disruption events and subsequent disc formation. Some work has been done on massive star binary mergers with low-mass companions, investigating the long term evolution of angular momentum as well as the surface abundances (Chatzopoulos et al 2020;Wu et al 2020). Tidal disruption events around white dwarfs have also been investigated (Malamud & Perets 2020;Veras et al 2014).…”